band bending

A simple thermal annealing at 150 °C followed by exposure to air ambient conditions in epitaxial ZnO thin films produces a photoconductivity enhancement and a reduction of the energy gap. The first effect is related to a release of carriers from bulk traps while the second is caused by a gradual adsorption of species on the film surface which increases the band bending, as x-ray photoemission spectroscopy (XPS) shows. An observed drift of the photoconductivity and the energy gap over the days is connected to this adsorption kinetics. These findings have a potential application in ZnO based optoelectronic devices.

We present a photoemission spectroscopy study of As-rich n-GaAs(001) surface modified by the deposition of an undoped silicon overlayer with thickness quite narrowly covering the interval from ~4 to 25 Å. We observed a nonmonotonic relation between the surface band bending and Si overlayer thickness with the lowest surface potential at about 10-Å-thick silicon overlayer. The valence band spectra inspection reveals the double leading edge incidental to alignment of the valence band edges of GaAs and Si overlayer with the offset of 0.29 eV and various theoretical models of semiconductor–semiconductor interfaces are discussed. Based on the influence of the silicon layer on both band bending and Schottky barrier height, it is concluded that the Schottky
barrier height of Au/Si/GaAs structure evolves towards the Schottky limit for an ideal (par definition free of interface states) Au/GaAs junction as the silicon interlayer thickness reaches about 10 Å.